With three wins out of three, the Rojiblancos are expected to reach the last 16, though the Argentine says he is concentrating on one game at a time
Raul Garcia gave the Rojiblancos the perfect start to the Group G encounter with an early goal, before a double from Diego Costa sealed a comfortable victory for the Liga outfit.
The win leaves Simeone's side five points clear at the top of the group with three wins from three matches, but the coach has called for calm despite excellent starts both in Europe and domestically - where they have won eight out of nine games.
"We cannot afford to move away from this game-by-game mentality," he said. "We know the difficulties we will face in the Champions League and in La Liga.
"It was a very good first half for us in terms of how we interpreted the way in which we had to control the game and its rhythm.
"Positioning Raul [Garcia] behind Diego Costa gave us a lot of strength, and our full-backs were also excellent."
Costa, playing in his first Champions League game after serving a two-match European suspension, took his season goal tally to 12, and he reiterated Simeone's message that the side are taking things one clash at a time.
"I felt good out on the pitch and was very happy to make my Champions League debut in such a manner," Costa said.
"We played a great game. Our way of thinking is to take things on a game-by-game basis, trying to reach our maximum level in each encounter."